Re: [PATCH v5] PCI: cadence: Retrain Link to work around Gen2 training defect.

[Rob Herring]

On Fri, Dec 18, 2020 at 8:42 AM Kishon Vijay Abraham I <kishon@xxxxxx> wrote:
>
> Hi Rob,
>
> On 16/12/20 10:31 pm, Rob Herring wrote:
> > On Wed, Dec 16, 2020 at 9:01 AM Kishon Vijay Abraham I <kishon@xxxxxx> wrote:
> >>
> >> Hi Rob,
> >>
> >> On 15/12/20 9:23 pm, Rob Herring wrote:
> >>> On Tue, Dec 15, 2020 at 1:00 AM Kishon Vijay Abraham I <kishon@xxxxxx> wrote:
> >>>>
> >>>> From: Nadeem Athani <nadeem@xxxxxxxxxxx>
> >>>>
> >>>> Cadence controller will not initiate autonomous speed change if strapped as
> >>>> Gen2. The Retrain Link bit is set as quirk to enable this speed change.
> >>>>
> >>>> Signed-off-by: Nadeem Athani <nadeem@xxxxxxxxxxx>
> >>>> [kishon@xxxxxx: Enable the workaround for TI's J721E SoC]
> >>>> Signed-off-by: Kishon Vijay Abraham I <kishon@xxxxxx>
> >>>> ---
> >>>> Hi Lorenzo,
> >>>> The previous version of the patch can be found at [1].
> >>>> I slightly re-worked the patch from Nadeem
> >>>> *) Removed additional Link Up Check
> >>>> *) Removed quirk from pcie-cadence-plat.c
> >>>> *) Also removed additional compatible
> >>>>    "cdns,cdns-pcie-host-quirk-retrain" added in that series
> >>>> *) Enabled the quirk for J721E
> >>>> [1] -> http://lore.kernel.org/r/20201211144236.3825-1-nadeem@xxxxxxxxxxx
> >>>>
> >>>>  drivers/pci/controller/cadence/pci-j721e.c    |  3 +
> >>>>  .../controller/cadence/pcie-cadence-host.c    | 67 ++++++++++++++-----
> >>>>  drivers/pci/controller/cadence/pcie-cadence.h | 11 ++-
> >>>>  3 files changed, 62 insertions(+), 19 deletions(-)
> >>>>
> >>>> diff --git a/drivers/pci/controller/cadence/pci-j721e.c b/drivers/pci/controller/cadence/pci-j721e.c
> >>>> index dac1ac8a7615..baf729850cb1 100644
> >>>> --- a/drivers/pci/controller/cadence/pci-j721e.c
> >>>> +++ b/drivers/pci/controller/cadence/pci-j721e.c
> >>>> @@ -64,6 +64,7 @@ enum j721e_pcie_mode {
> >>>>
> >>>>  struct j721e_pcie_data {
> >>>>         enum j721e_pcie_mode    mode;
> >>>> +       bool                    quirk_retrain_flag;
> >>>>  };
> >>>>
> >>>>  static inline u32 j721e_pcie_user_readl(struct j721e_pcie *pcie, u32 offset)
> >>>> @@ -280,6 +281,7 @@ static struct pci_ops cdns_ti_pcie_host_ops = {
> >>>>
> >>>>  static const struct j721e_pcie_data j721e_pcie_rc_data = {
> >>>>         .mode = PCI_MODE_RC,
> >>>> +       .quirk_retrain_flag = true,
> >>>>  };
> >>>>
> >>>>  static const struct j721e_pcie_data j721e_pcie_ep_data = {
> >>>> @@ -388,6 +390,7 @@ static int j721e_pcie_probe(struct platform_device *pdev)
> >>>>
> >>>>                 bridge->ops = &cdns_ti_pcie_host_ops;
> >>>>                 rc = pci_host_bridge_priv(bridge);
> >>>> +               rc->quirk_retrain_flag = data->quirk_retrain_flag;
> >>>>
> >>>>                 cdns_pcie = &rc->pcie;
> >>>>                 cdns_pcie->dev = dev;
> >>>> diff --git a/drivers/pci/controller/cadence/pcie-cadence-host.c b/drivers/pci/controller/cadence/pcie-cadence-host.c
> >>>> index 811c1cb2e8de..773c0d1137ed 100644
> >>>> --- a/drivers/pci/controller/cadence/pcie-cadence-host.c
> >>>> +++ b/drivers/pci/controller/cadence/pcie-cadence-host.c
> >>>> @@ -77,6 +77,50 @@ static struct pci_ops cdns_pcie_host_ops = {
> >>>>         .write          = pci_generic_config_write,
> >>>>  };
> >>>>
> >>>> +static int cdns_pcie_host_wait_for_link(struct cdns_pcie *pcie)
> >>>> +{
> >>>> +       struct device *dev = pcie->dev;
> >>>> +       int retries;
> >>>> +
> >>>> +       /* Check if the link is up or not */
> >>>> +       for (retries = 0; retries < LINK_WAIT_MAX_RETRIES; retries++) {
> >>>> +               if (cdns_pcie_link_up(pcie)) {
> >>>> +                       dev_info(dev, "Link up\n");
> >>>> +                       return 0;
> >>>> +               }
> >>>> +               usleep_range(LINK_WAIT_USLEEP_MIN, LINK_WAIT_USLEEP_MAX);
> >>>> +       }
> >>>> +
> >>>> +       return -ETIMEDOUT;
> >>>> +}
> >>>> +
> >>>> +static void cdns_pcie_retrain(struct cdns_pcie *pcie)
> >>>> +{
> >>>> +       u32 lnk_cap_sls, pcie_cap_off = CDNS_PCIE_RP_CAP_OFFSET;
> >>>> +       u16 lnk_stat, lnk_ctl;
> >>>> +
> >>>> +       /*
> >>>> +        * Set retrain bit if current speed is 2.5 GB/s,
> >>>> +        * but the PCIe root port support is > 2.5 GB/s.
> >>>
> >>> If you don't have the retrain quirk, wouldn't this condition never
> >>> happen and then the function is just a nop? So this could just be
> >>> called unconditionally.
> >>
> >> Yeah, but only for the quirk we have to retrain to go to GEN2 speed
> >> mode. Else the HW will automatically retrain and go to GEN2.
> >
> > Again, so you don't need a flag for this. Comparing the speed is
> > enough. IOW, all you need is:
> >
> > if (current speed < advertised speed)
> >   do retrain
> >
> > The question is the condition ever true and you don't want to do a
> > retrain? I could see higher speeds being unstable or something, but
>
> For all GEN1 cards there will be re-train (since the Cadence IP RC is
> GEN2 or more say). This is going to be true for older Cadence IPs and
> newer Cadence IPs (where Cadence has enabled HW re-training).
>
> The quirk will prevent SW re-training for newer Cadence IPs when a GEN1
> card is connected.

Okay, got it.

Reviewed-by: Rob Herring <robh@xxxxxxxxxx>